Method of and apparatus for quantitative gas analysis



Feb 26, l935 E. w. GILLILAND ET AL METHOD OF AND APPARATUS FOR QUANTITATIVE GAS ANALYSIS Filed Sept. 14, 1951 2 Sheets-Sheet 1 RATE 0F FLOW lNVENTORs 247/ awy 7M' a@ WW1/f.

WITNESSES may@ .Z/J'M Feb. 26, 1935. E. w.'G|| |LAND ET Al.

2 Sheets-Sheet 2 Filed sept WITN ESSES @d/@Mee A ..2

ratente Feb. ae, ieee METHOD on 1.992,'147-'v AND APPARATUS Fon 4 fs "series QUANTITATEVE GAS ANALYSES Ena'sw. Gilliland and, stanley D. Price, jPitts--` burgh, 'Pa., assignors to. Mine Safety Appliances Company, Pittsburgh, Pa., -acorporaticn Alternatief; september 14,1931, serrati No. 562,715. y

1e claims. 1 (o1. .as-238) This invention relates te the quantttatite analysis 4oi gases by.. means of catalysts, and

especially tothe determination of carbon monoxide in4 particularly of air vitiated by exhaust .gases from internalcombustiori engines.

A particular' application of apparatus for` quantitative 'analysis Aor `constituents of'gases is in the determination of carbon monoxide This -is importantyfor ;instance, VWhere air may be contaminated by Yexhaust gases from internal combustion engines, .as in passenger busses, Where the air may become vitiated by leakage of exhaust gas into the bus, especially in the, case of bus compartments heated by exhaust from the engine. Also, personsY carriedwby aircraft may be exposed to dangerous concentration of carbon monoxide resulting from the exhaust gases of their engines.

There have been available apparatus for. quan-y titatively measuring carbon .monoxide and other. combustible constituents of gases,v which make use of catalysts. The heatv change due to catalyticaction is 1used as a` quantitative measure of the proportion of constituent, and it is measured by means of one or more therrnocouples associated with the catalyst as a'h'ot junction. The cold junction has been composed of any material Y Whichdoes not cause'heat change when in contact with the gas, Yp'urnice being the material usually used. Apart `f-1 rorn the limitationl just mentioned, noV attention' hasbeen paid toV the cold `junction material. In-such apparatus the direction. of gas ovf has usually "been straight through a body of pumiee or the llike (cold junc-V tion) in contact with the catalystbed'.

Apparatus of catalytic type available heretofore hasbeen satisiactory `for sorne purposes,

` but experience has shown that under some conditions it .does not function properly. Thusit is not suitablefor use in determining carbon monoxide in airplane cabinsor cockpits, etc., Where operationoi the craft subjects itto rapid changes of temperature and 'atmospheric pressure'as the craft changesaltitude rapidly. Under these and other vcircuinstances .prior apparatus functions inaccurately, either indicating the' Y presence of carbon n'ionoxide when it is not actuserious results.

Vally present,` or in` amounts different from .that

actually present. Such inaccuracy may entail Nor has vthere 'been available a portable 'apparatus 'for determining. such constituents with. high t. accuracy over Wide ranges.V

of. concentratior-i,` @runder widely varying operating conditions.

It'` is. amongV the objects. of this invention to provide an improved method of 'and apparatus for Vthe quantitative determination of a combustible Azzoristituent ofa gas bymeans of catalysts',

which aresiinple, readily used, do not require complicated apparatus, are adapted for highly accurate determination of Very small concentrav tions, aswell as large amounts, of such constitu-. ents, and are adapted to provide accurate results. irrespective of and under Widely varying-operating conditions. f

A particularobject is to provide a method and apparatus of the type described Whicha're espe-j cially adapted for use in determining the presi-- ence and extent of carbon-monoxide vitiation oiA air by internal combustion exhaust gases, espe-r cially for portable use in aircraft.4 f The invention is illustrated in the accompanying draWings which represent its preferred ern-5. bodiment, and in which Fig. lisa diagrammatic representation of the apparatus; Figs. 2 and 3 longitudinal sections thro-ugh elements of` the apparatus shown fin Fig. 1; Fig. 4 a fragmentary section of a portion of the apparatus shown in Fig. V3, taken on line IIT-III; Fig. 5V a fragmentary section taken on line V-V, Fig. 1; Fig. 6 a graph representative of therelation vbetweenrate of gas flow through it; and Figs. 7 and 8 Wiring diagrams of the apparatus shown in Fig. 1-.l

The temperature-rise. due to the catalytic come "bu-Stien of such constituents, especially when in air, is generally quite small; sothat'its inaccurate' measurement may cause substantial inaccuracy in the result. We have discovered that the inability or' these'apparatus to function satisfactorily as previously constructed is due to the fact 1 that the true jttemperature changes inthe catalyst bed cannot :always .be measured exactly. For inistance, they cannot accurately `fu'nctionfunder" varying operating conditions, such as experienced by aircraft. Wehave found this to be due to the fact that theA hot and' cold ijunctions of AtheY catalyst do notchangein temperature' at the` same rate'when the apparatus is exposed to a change in temperature.. 'l'l'ius,the` catalyst, con;` stitutingrthe hot junction of the thermocouple, changes temperature at a rate different from thatof the .pumice or other material usedv as the' cold junction.. 4This difference in rate of heat transier betweenk the atmosphere on the onehand and the hot and cold junctions on the other` as the apparatusY is subjected to changing temperatures causes thev thermocouple'to-indicate. a Vfalse result;`

Y since 'the instrument has-been calibrated for junctions. For instance, if anwairplane equipped with such apparatus rises from the earth to a high altitude, and the cold junction material loses heat more rapidly than the catalyst material, the thermocouple will not indicate the true temperature in the, catalyst, and quanitative measurement of carbon monoxide actually present is not possible. Y

This factor has not previously been recognized, any indifferent cold junction material beingused on apparatus in which the'gas passes directly through catalyst and cold junction beds afurther source of inaccuracy has been vdue to transfer of heat from the catalyst tothe cold junction material. The effect of this is, of course, to cool the former and heat the latter, rendering the thermocouple readings inaccurate. This is especially serious because of the low temperature gradient between the two junctions, which may not exceed 17 C. with some concentrations of CO.

We have discovered further, and it is upon this that our inventionY is predicated in part, that these disadvantages may be overcome, and highly accurate results 'assured under widely Varying operating conditions, by providing hot and cold junctions of substantially the same thermal properties. In accordance with the invention, therefore, the hot and col'djunctions change temperature at the' same rate when the apparatus is exposed to changing temperature, and this maintains correct relationship between the two junctions. This provides for continuous accurate Vmeasurement of the temperature change caused by the action of the catalyst upon a combustible constituent'in the gas passed through it, irrespective of changing external conditions.

We have discovered alsothat the sensitivity and accuracy of the apparatus may be further improved by minimizing heat transfer between the hot and cold junction materials. This is accomplished in accordance. with this invention by arranging the lhot and cold junction materials as separate elements, and preferably also by interrupting direct iiow between `the two beds, most suitably by passing the gas through the elements in opposite directions, in contrast to the straight through flow of prior apparatus.

Catalyst and cold junctionV beds having the same thermal properties may be provided in va- 'rious'ways but the most satisfactory results are Vobtained by using as the cold junction a bed of the catalyst material in an inactive or spent condition. In this manner the hot and coldrjunctions of .the thermocouple are embedded in the same material, the 'former being catalytically active, and the latter catalytically inactive, 'to the constituent to be determined. f Thus they are of the same thermal conductivity, and by making the beds of substantially the same size, they have the same heat capacity.

The rate of heat transfer -is governed in part by the conductivity of 'a'materiaL so that this `factor `appears to be of importance here. VHowever, the heat capacity appears to play a part also. In the absence of denite information as to which, if either, of these properties is controlling, the term "thermal properties is Vused herein for brevityof reference. Y Y

The invention provides also Van apparatus for the practice of the method just described, and in addition this apparatus embodies other features presently to be described, which constitute an improvement `upon prior apparatus of this type. The method may be understood further, and the apparatus described, with reference to the accompreferred from which it flows through aline 8V to pump 1 which exhausts the gas to the atmosphere through an exit line 9 and check Valve 9a.

Drier 5 preferably comprises an ordinary gas mask canister, Fig. 2, preferably of relatively large capacity, having inlet and outlet couplings 10 and 11,` and containing a granular drying agent 12, such as calcium chloride, or calcium chloride and activated alumina, held between wire screens 13 in the manner customary in such devices. Its

-purpcse is to prevent poisoning of the catalyst by moisture.

'In accordance with the invention the gas isV passed through a catalyst vcell which contains separate beds of catalyst and cold junction material of substantially the'sarne thermal properties, and in which there Vare embedded respectively the hot and cold junctions of a thermocouple. The beds are separated to prevent heat transfer vfrom the catalyst to the cold junction bed, most suitably by so constructing the cell as to cause the gas leaving the cold junction bed to change its direction of iiow and pass through the catalyst bed in the opposite direction.

The embodiment vof cell 7 shown comprises a tubular casing 14, Fig. 3, provided with inlet and outlet coupling members 15 and 16 connected respectively to lines 6 and 8. Disposed within casing 14 is a tube 17 spaced from the shell by a ring 18 of any suitable material. Tube 17 is divided transversely into` two compartments by means of a disk 19, preferably ofV heat insulating character, held inY position by screws fastened to shoulder 20 interiorly of the tube. On opposite sides of disk 19 there areconnected to the tube Vrings 21 which hold a tubular screen member 22 in iixed position spaced from the interior-wall of the tube. The ends of the casing are closed by caps 23 threaded into the casing, as shown.

In this'construction the cell contains annular passages 24 and 25 between the casing and tube, which are separated by ring 18. Passage 24 opens into inlet coupling 15,` and into the adjacent chamber`Y 24a of the tube.A vOpposite screen 22 at the base .of chamber 24a is a perforation in Athe wall of the tube, connecting the chamber with passage 25, and this latter opens into the chamber 25a formed in tube 17 by disc 19. Exhaust coupling 16 is connected to chamber 25a, as shown. l

A deep bed of inactive, or spent, catalyst is disposed in chamber 24a, to act as cold junction material, and chamber 25a is lled with the same material in a catalytically active condition. The beds contain approximately the same amount of material, soV as to be of liketherrnalproperties. 'Ihe catalyst preferably comprises hopcalite where CO is to be determined, and for the cold junction spent hopcalite may be used, or the activity of hopcalite may be destroyed for this purpose. V

The beds of 'catalyst and' cold junction material are maintained in position by means of screens 27 urged inwardly by springs 28 acting belike may be removedr -from the gas before it reaches the.@ta1yst-byae1terl29 @gauze-held in place bya screen 29a, as shown.V

In` order-.xtc c leterrnine the temperature change causednbythe action of the` catalyst upon -ia rconi-A p bustible constituent of the gas, such as CO, therrnocouple is mounted in the cell withjitscold junctionin the inactive material inchamber 24a,

andits hotjunction in the catalyst., Dependent upon the accuracy required, one or rnore'therrnm couples may be usedthe sensitivity'being increasedfby the usev of `a thermocouple'nnit of. a

Vplurality of couples connected in series. Suchan arrangement is shown in Figs. 3` and` 4, whichv a plate 31, of micaor the like sealed in disci'19,` through which it passes, acts as a support for a plurality of thermocouples iconnected inseries and'having their opposite ends embeddedas de? scribed. i i. i

. In. the Vpreferred embodiment, the, thermocouples .comprise Chromel wires 32 andConstantan wires 33, Fig.V 4; Bytheuse .of a thermocouple of this type comprising ftyeve such couples seriespand using-'hopcalite as `the catalyst, `.the apparatus is capable of' determiningV up to about 0.15 percent-cf CO with an accuracy or 0.01 .per-

`cent of CO.:Y By appropriately increasing or'decreasing the number of .thermocouples, the sensi-` tivity andrange of the apparatus'rnay bechanged according to need. Y 4 AThe construction 4shown andudescribed providesfor ilow `of gas through the coldjunction and thence tdthe catalyst in a" counterdirection,"

as indicated by the arrows ,in Fig. 3'. `.as there shown, dried gas from'drierl 5 enters through cou-` pling l5' into annularspace24, and Ailcvvs through the inactive bed Ziaywhence itpasse's-'out through:

Y Vscreen22 and cpeningintoannular space 25 on the opposite side ofxring 13.3'Ih'e gas then lowsthrough catalyst bed 25a ,'where'the.CO is oxidized, andV it leaves through outlet coupling 15.

" Fernse as=a portable instrument, or in a permanent installation, such as in a vehicular tunnel, or

on an aircraft, .the ends of the-,thermocouplesfarfe connected vto leads "34 and vconnected "to ."a

- galvanometerhaving its scale. graduatedto read directly in percentagefof CO. If desired, the thermocouplerinay be connected to a` signalling device, suchas a bell 37, -or toM a graphicrecorder,Y of which several types are available;V

Drier prevents access of mo-istureto the catalyst troni the inlet end of the apparatus, andfor the same purpose pump 1 is provided withal@- automatic check valvewhich closes. theexlfiaust ,line when the apparatus is lnot in use;` One form ci valve'isshov/n Vir'rliig. 5. It comprisesl a hollow housing 38 connected to exllaust'ioipe 9, and,`

within -the housing there is alightaweightidisc 39. When the pump is operating, disc 39 is forced upwardly against studs fioiformed on inwardly extending Vflanges 33a, permitting the gasto be exhaustedto the atmosphere. When the pump ceases toroperate the disc fallsand closesV the. e5;- haust line. Guard in e'rnbers 41 Vprevent externalV injury to discl 39;

l `The accuracyand sensitivitycf the determina-f" tionsrare also dependent uponthe rate 'of -flovv ofV gas through theV apparatus,V and this may bein-" financed' by variation in atmosphericV pressure;

Itheotlier pole being connected 'f r In the use of the apparatus gas nated.; Having reference' to` -Eig. 6, the variation of, thermocouplc E. NL F. with the Vrate of. flow of `gasthrough the` catalyst was Aplotted for aV v given concentration of CO in air.` With iow rates of nov/the E. increases rapidlyV as therate Y offlow increases. Undersuch conditions changes Y in altitude "'wouldfseriously affect the results. However,` our tests demonstrated, as VFig. 6 shows,"that-within certain ranges oiflowrate its variation Adoes not exert any substantial change` inpotential recorded `by the ltherrnocouple.. We

have found that, inV general, ratesof flowV from-v about )3.5 to 5 liters per minute satisfactorily .overcome the diniculty referred to, a rate'offil/g liters per` minute being preferred. x

` In order to insure constancyV of Iilo-vv rate Vunder varying. conditions 'pump 1 Ypreierably -cornprises at rotary positive pressure blower type. For thisV use theblovfer` duty is not heavy, soV that it V'n xayvbe operatedby means of a motor Vrun from anordinary six Voltstorage `celljth'us making it.

possible-Zizo`r provide aportable type apparatus;

since most automotive-vehicles and aircraft use the inlet of. the blower is connected to theoutlet of cell 7. Regulation of the iovv rate within theVV limits given, to maintain'substantial ccnstancy of flow, is provided for by means oithe manometer 4, its scale beinggraduated appropriately 1 v1 In the `use of this apparatus'athigh altitudes,`

i..e.,'at\low temperaturesfithas been .found that suchbatteriea- .Being used Las an exhaust pump, i

thefblowerstarts sluggishly, owing Ito chilling of-' 'i fthegrease.` .Thismay-be overcome by providing theblower with a heating', element.V Thewiring diagram, for the motor and heating elementare Vshown in Fig-"fl, Current is'suppliedtofmotcr 2-V fromacurrentjsource 42 by'meansof a lead. 43,

and a leadietconnected to onepole oi'adouble-J "throw single-pole switch 45, the other pole being' connectedby a; lead V4:6 tojthe otherside of the motor;V In ordery to control 'the heating circuit,

`-lead (Ms also connectedtoone poleoi anotherL switch liiovvhich controls a-heatng element 471';V arranged -to heat the'grea'se in pump l, this C'f" cuit returningto thelurrent source by a' lead e8. i i Theindicating circuit is shown in Fig. 8,in

which' therrnccouple lead 34irorn cell 7 is connected to 'galvanorneter 36 through; one terminal lof jackligi 'The other Jlead,35,n is connected to one sidefof a `double-.pole double-throw-switch 'connectedY bya lead 51 to theother side ofthe galvanorneter. #1A shunt-.52'connects lead 135 also toone pole-,ori the opposite-side ofthe switch, f

by a lead 53 to the other terminal ofthe jack.

Where the apparatus Visembodied in aportableV instrument galvanorneter 36 forms a permanent A part thereof. f'Jack 49, however, ,provides for con-. necting the cell'toa recorder,` alarm signal, o rthe like, according to need.

drawn continuouslyfinto sampling. line 3, Vand V'passes through d rier Vvto cell 7, Where the comu vbustible constituent Whichis to Vbe determined i is burned by thecatalyst. .'The rate of flow is 'regulated'rea'dily `by.j,obser-vation of Ymanom'eter ijfand' regulationY of 'thepump operation accord-g, ing'ly;V Changes'in theoper'ating conditionsjsuch as-sudden variationsfin temperature, are without 'Y eiectupon the results obtained, because uponthej occurrence of a change in 'temperature both thev hot and cold junctionsabsorb or give oiheat, asV

,the` casefrnayrbe;` at substantiallyV the same rate,A

and theaccuracy of? the reading Visnot affected.,

so that their relative condition remains,constantl Vchanging operating conditions.

-tion of heat of combustionin the hot junction bed, providing for accurate results.

Moreover, because the potential readingis' in- Y dependentV of change in rate Yof flow within the optimum range, this factor does not aiect the results. Thus, the invention renders it possible to obtain'highly accurate determinations of a constituent under Widely varying and rapidly The invention has particular value in connec "tion with carbonvmonoxide controlin aircraft,

although kit may be used equally with automotive vehicles, vehicular tunnels, and in other locations. Because the apparatus is simple, Vand portable, it

rmay. be usedreadily with airplanes to determine the presence of CO, in its cabin, etc., as a basis for designing, or redesigning, such craft toavoid CO contamination of the air which reaches/its passengers. .'Likewise, in passenger busses, large passenger airplanes, dirigibles, or the lil:e',it` may be mounted in xed position and operated continuously, the occurrencein the air of va xed minimum percentage of CO actuating alarm signal3'7.

According to the provisions of therpatent statutes, we have explained the principleand mode of operation of our invention and have illustrated and described what we'now consider to represent its best embodiment. However, we' desire to have v'it understood that, within the scope ofthe appended claims, the invention' mayY be practiced otherwise than as specifically illustrated and described. v

`Weclairn: s' v.

l. In a method of quantitatively deternfiining a combustible constituent of a gas, the steps comprising passing said gas successively through separate bodies of material Ythermally Yinsulated from each other and-having substantially the same thermal properties, oneof said bodies being catalytically inactive and the other catalytically active to said constituent, and measuring the temperaturechange due to catalytic action by thermocouple havingits hotV and cold junction associated respectively in said active and inactive bodies.

. 2. Ina methodoi quantitatively determining a combustible constituent ofragas, the stepsY comprising passing said gas through a body of material catalytically inactive to saidconstituent, and Athen passing it through a body of oxidizing catalyst separate and vthermally insulated from said inactivefnaterial, said bodies having sub-V stantially the same thermal properties, and measuring the temperature change by'a'thermocouple having its hot junction incontact with` said catalyst material, and its cold'junction in contact with said inactive material.

3. A continuous method of determining a con' stituent of a gas, comprising Adrying the gas andAY passing itcontinuously through a body of maf terial'catalytically inactive to said constituent, and then passing itincountercurrent direction through a separate bed of the same material in a condition to catalytioally causeachange of Asaid constituent, saidv bedsbeing of substantiallythe r same thermal properties and being thermally in'-v sulated from each other, and measuring the tem-- perature change in the catalytieallyV active 'bed by'a plurality Vof thermocouples connected in se- Y ries and havingtheir hotand coldjunctionsemAV bedded respectively in the catalytically activeand inactive beds.

4. A method' of quantitatively determining l a of substantially the same thermal properties,

measuring the temperatiu'e change in said active vmaterial Yby a thermocouple having-its hot and cold junctions embedded respectively in vsaid active and inactive material, and regulating the Vrate of flowto render the temperature effect in the active. bed independent pressure of the gas.

o f changes inthe 5. A method of quantitatively determining a combustible constituent of a gas, comprising passa ing said gas successively through separate bodies of an oxidizing catalyst respectively in catalytically inactiveand catalytically active condition, said bodies being thermally insulated fromA each other and having substantially the samethermal properties, measuringY the temperature change in said active body by a plurality of thermocouples having'their'hot and coldjunctions associated respectively in said'active and inactive bodies, and regulating the rate of iiow within the range in which the temperature effect in said active body is independent of changes in pressure of the gas.

6. Apparatus for quantitatively determining a constituent oi' a gask comprising a Vcontainer provided with a gas inlet. and a gas outlet, separate bodiesof the same material in` catalytically'inactive and catalytically active condition with respect to said constituent'arranged in the path of the gas'in the container adjacent Vsaid gas inlet and outlet respectively-'for successive passage of the gas therethrough, said bodies being of substantially like thermal properties, a partition between said bodies separating and heat insulating them 4.from each other, means for passing the gas from the inactive tov the active body, and means for having' their hot andf'cold junctions embedded respectively in said active and inactive material; 7. Apparatus for quantitatively determining a constituent of a gas comprising a container pro' vided with a gas inlet and a gas` outlet, a cata- Y measuring the temperature insaid active bed including a plurality of thermocouples in serieslytically inactive material arranged inthe path of gas adjacents'aidinleaa separate body of catalyst active with respect .to said constituent arranged in the path ofthe gas adjacent said outlet, a partitionV between said bodies separating and heat insulating themvfrom each other, means for passing gas from said `inactivematerial through saidcatalyst in 'countercurrentdirection,`

and means formeasuring the temperature in the catalyst bed including a thermocouple having its hot ,andfcold junctions embedded respectively in said catalyst and inactivematerial, said bodies inactive catalytic material varranged in the path ofgas adjacent said inlet, a separate body of the same material'in catalytically active condition with respect to said constituent'arranged in the path ofthe gasadjacent said outlet, said bodies 'being of substantially like thermal'p'roperties, a

partition separating and heat insulating said inactive andactive catalystbodies from each other, means for passing gas from said inactive material through said active material in countercurrent direction, and means ,for measuring the nocaut temperature-in 'the catalyst bed including aplu; rality of thermocouples in series `leaving their hot and cold junctions embedded respectively in said active catalyst and inactive material.

9. Apparatusgfor continuously and quantitativelydetermining a constituent of a gas, comprising a container provided with a gas inlet and a gas outlet, means Vfor drying gas passed to said container, a body of inactive catalyst in the path ofgas adjacent said inlet, Ya body of the same material in catalytically active condition vWith respect to said constituent in the path of gas adjacent said inlet, said bodies being of substantially the same thermal properties, a partition separating and heat insulating said bodies from each other, means for passing the gas in countercurrent directions through said bodies, means for measuringVV the temperature in said catalyst body comprising a thermocouple having its 'hot and cold junctions embedded respectively in said active and inactive material, and a positive pressure blower associated with said outlet to draw gas through the container at a substantially uniform y rate of flow,

y l a combustible'constituent of va gas, the steps com- 10. In a method of, quantitatively determining prising passing a sample of said gas successively through separate bodies of (1) material` catalytically inactive With'respect to said 4combustible constituent and (2) an oxidizing catalyst,.said bodies being thermally insulated from each other and having substantially the same thermal caj pacity, and measuring the temperature change in ,said active body due to its catalytic action on said constituent by a plurality of thermocouples conl Lnected in series and having their hot and cold junctions associated respectively with said active and inactive bodies.A

11. Apparatus for quantitatively determining a constituent of `a gas comprising a container provided With a gas inlet and a gas outlet, separate beds of material respectively in catalyti- `cally'i'nactive and'catalytioally active condition with respect to said constituent and of substan- 'tially'identioal thermal properties arranged'in the path of the gas in the container adjacent said gas inlet and outlet respectivelyV for successive passage of the gas therethrough, a partition separating and heatinsulating said beds from each other, means for passing the gas from said inactive to said active body, and means .for measuring the temperature in the active bed including a thermocouple having its hot and cold junctions embedded respectively in said active and inactive beds. l v "Y Y 12. Apparatus for quantitatively determining a constituent of a gasl comprising.` a container throughwhich said gas is passedgseparate beds of material catalytically inactive and catalytically active With respect to said constituent and of sub.- stantially identical thermal properties arranged respectively in the path of gas Vthrough `the container for successive passage of the gas .therethrough, partition'meansseparatmg and heat insulating said beds from each other, means for measuring the temperature change in the active bed including a thermocouple having its hot and cold junctions embedded respectively inrsaid active and inactive beds, anda rotary positive blower connected to said container to draw said gas therethrough at a substantially uniform rate;

13. In a method of quantitatively determining` material catalytically inactive to said constituent,`

- ing` the gas rial, said bodies being of Vsubstantially the saine thermal properties, and measuring the temperature change in the catalytically active body by a therniccouple having its cold and hot junctions lyst thermally insulated from said inactive mateembedded respectively in said inactive and catalyst bodies..

14. In method of quantitatively determining a combustible constituent of a gas, the steps comprising passing said gas first through a body of oxidizing catalyst in inactive condition, then passin the opposite direction through a separate catalytically active body of the catalyst thermally insulated from said inactive material, said bodies Vbeing of substantially the same thermal' properties, and measuring the. temperature change in the catalytically active body by a plurality of thermocouples having their cold and hot junctions embedded respectively in said inactive and active catalyst bodies.

15. In a-method of quantitatively determining vpassing the airlthrougha bed of inactive oxidizing catalyst, then passing the same air in the opposite direction through a separate body oi said catalyst in active condition and thermally insulated rorn said inactive material, said bodies being ofV substantiallyV the same thermal properties, and measuring the temperature change in the catalyticaliy active body by a plurality of thermocouples having their cold and hot junctions ernbedded respectively in said inactive and catalyst bodies. Y

16. A continuous method of quantitatively determining a constituent of a gas, the steps cornprising `contirniously passing said gas through a body of material Vcatalytically inactive to said constituent, then passing the same gas in the opposite directionV through a separate bodyof the same material in a condition to catalytically cause a change' of said constituent,V said bodies being thermally insulated from each other andbeing of substantially the same thermal properties, and measuring the temperature change in the cata- -lytically active body by a thermocouple having its Vcold and hot junctions embedded respectively in said'inactive and catalyst bodies.

1'7. A method of quantitatively determining a combustible constituent in mixture with air, comprising passing the air through a body of oxidizing catalyst in inactive condition, then passing the same air. in the opposite direction through a separate body of the same material in catalytically active condition with respect to said combustible constituent, said bodies being thermally insulated from each other and havingsubstantially the same'thermal properties, measuring the temperature lchange due to catalytic action by ai' plurality of thermocouplesconnected in series and having their hot and cold junctions associated respectively with said active and inactive bodies, and regulating the rate of flow Within the range in which the temperature effect in said active body is independent of changes in atmospheric pressure.

18.Amethod of quantitatively Vdetermining carbon monoxidein air, comprising drying the air and passing it through a body of oxidizing catalyst in inactive condition, then passing the same air in the opposite direction through a separate body of said catalyst in catalytically active condition with respect to carbon monoxide, said ybodies being thermally insulated fromeach other and having substantially the same thermal properties, measuring the temperature change due to catalytic action by a plurality of Ythermoeouples connected in series and havingI their hot and Vcold junctions associated respectively with said .active and inactive bodies, and regulating the 

